POSITIONING MOTORS BY MEANS OF CAPACITIVE MEASURING

Abstract

A measuring arrangement and corresponding method for determining the rotational position, speed and/or direction of rotation of a shaft, in particular of an electric motor of an electromotively adjustable device of a vehicle. The measuring arrangement comprises at least first and second electrodes which each form capacitor elements, wherein an electrical voltage can be applied to the electrodes to generate an electric field (EF); a rotatable shaft, in particular a motor shaft, having a measuring section which has an out-of-roundness, wherein the measuring section is arranged relative to the electrodes such that a rotation of the shaft changes the electric field (EF); and an evaluation unit which is conductively connected to an electrode to capacitively capture a change in the electric field (EF), in particular in the form of a change in a voltage applied to an electrode.

Claims

1. Measuring arrangement for determining the rotational position, speed and/or direction of rotation of a shaft of an electric motor of an electromotively adjustable device of a vehicle, comprising: at least one first electrode and at least one second electrode which each form capacitor elements, wherein an electrical voltage can be applied to the at least one first and at least one second electrodes in such a manner that the at least one first and at least one second electrodes generate an electric field (EF); a rotatable shaft having a measuring section which has an out-of-roundness, wherein the measuring section is arranged relative to the at least one first and at least one second electrodes in such a manner that a rotation of the shaft changes the electric field (EF); an evaluation unit which is conductively connected to an electrode and is designed to capacitively capture a change in the electric field (EF), in particular in the form of a change in a voltage applied to an electrode.

2. Measuring arrangement according to claim 1, wherein at least first and second electrode pairs each comprising at least one first and at least one second electrodes are provided, wherein the first electrode pair is designed to determine the rotational position and/or speed of the shaft and the second electrode pair is designed to determine the direction of rotation of the shaft.

3. Measuring arrangement according to claim 1, wherein the measuring section of the shaft has a shaft profile which is not rotationally symmetrical.

4. Measuring arrangement according to claim 1, wherein the shaft profile has radial measuring elevations distributed over the circumference.

5. Measuring arrangement according to claim 1, wherein at least two measuring elevations extend to a different degree in the radial direction.

6. Measuring arrangement according to claim 1, wherein the shaft profile is a toothed profile or a polygonal profile, wherein the shaft profile has 2 to 16 radial measuring elevations.

7. Measuring arrangement according to claim 1, wherein the shaft axis is arranged parallel to a central plane (PM) of the at least one first and at least one second electrodes, preferably perpendicular to an electrode plane (PE) in which the at least one first and at least one second electrodes are arranged.

8. Measuring arrangement according to claim 1, wherein the measuring arrangement comprises a printed circuit board on which the electrodes are arranged.

9. Measuring arrangement according to claim 8, wherein the printed circuit board has a measuring recess, wherein the measuring section of the shaft extends into the measuring recess.

10. Measuring arrangement according to claim 1, wherein the measuring arrangement comprises a microcontroller which is designed to supply at least one of the at least one first and at least one second electrodes with a DC voltage.

11. Measuring arrangement according to claim 1, wherein the evaluation unit comprises a filter unit which is designed to allow a frequency band of a captured measurement signal to pass through.

12. Measuring arrangement according to claim 1, wherein the measuring section is electrically conductive.

13. Measuring arrangement according to claim 1, wherein the shaft is a motor output shaft of an electromotively adjustable device of a vehicle.

14. Method for determining the rotational position, speed and/or direction of rotation of a shaft of an electric motor of an electromotively adjustable device of a vehicle, comprising the following steps: a) providing at least one first electrode and at least one second electrode which each form capacitor elements; b) applying a voltage to the at least one first and at least one second electrodes in order to generate an electric field; c) rotating a shaft which has a measuring section with an out-of-roundness, wherein the measuring section is arranged relative to the electrodes in such a manner that a rotation of the shaft changes the electric field (EF); d) capturing the change in the electric field (EF) by means of a capacitive measurement using an evaluation unit which is conductively connected to at least one of the at least one first and second electrodes by capturing a change in a voltage applied to the at least one of the at least one first and second electrodes; e) determining the rotational position, speed and/or direction of rotation of the shaft with the evaluation unit on the basis of the captured change in the electric field (EF).

15. Use of a measuring arrangement according to claim 1 for determining the rotational position, speed and/or direction of rotation of a shaft of an electric motor of an electromotively adjustable device of a vehicle.

16. Measuring arrangement according to claim 1 wherein the measuring section of the shaft has a shaft profile which is point-symmetric with respect to the shaft.

17. Measuring arrangement according to claim 1 wherein the measuring section of the shaft has a shaft profile which is point-symmetric with respect to the shaft axis and has at least one radial measuring elevation.

18. Measuring arrangement according to claim 10, wherein the DC voltage is a pulsed DC voltage.

19. Measuring arrangement according to claim 1, wherein the shaft is a motor output shaft of at least one of a sliding roof, a window lifter, an exterior mirror, a seat, a convertible roof or a locking mechanism.

20. Measuring arrangement according to claim 1, wherein the shaft profile has radial measuring elevations uniformly distributed over the circumference.

Description

[0041] Exemplary embodiments of the disclosure are explained in more detail below on the basis of the drawings, in which:

[0042] FIG. 1A shows a schematic illustration of a first embodiment of a measuring arrangement according to the disclosure, wherein the shaft is in a first rotational position;

[0043] FIG. 1B shows a schematic illustration of the embodiment according to FIG. 1A, wherein the shaft is in a second rotational position;

[0044] FIG. 2 shows a schematic illustration of a second embodiment of a measuring arrangement according to the disclosure having two electrode pairs.

[0045] In the following description of the disclosure, the same reference signs are used for identical and identically acting elements.

[0046] FIGS. 1A and 1B show a measuring arrangement 100 according to the disclosure for determining the rotational position, speed and/or direction of rotation of the rotatable shaft 10 in a first and a second rotational position. A first electrode 20 and a second electrode 30, which each form capacitor elements, are arranged in an electrode plane PE in a symmetrical manner with respect to a central plane PM (perpendicular to the electrode plane PE or plane of the drawing in the figures). The electrodes 20, 30 form capacitor elements which are flat at the ends and are formed here, in the form of plates with a rectangular basic shape, from a conductive, in particular metallic, material, for example copper. The shaft axis 12 of the shaft 10 is perpendicular to the electrode plane PE and runs in the central plane PM. An electrical voltage is applied to the electrodes 20, 30 and generates, in the environment of the electrodes 20, 30, an electric field EF, the field lines of which are indicated as dashed lines. FIG. 1A illustrates the electric field EF in a reference state, that is to say substantially without interference, whereas FIG. 1B illustrates it in a changed or disrupted state, which is illustrated, in particular, by the deformed field lines.

[0047] The shaft 10 has a measuring section 11 with an out-of-roundness in the form of the shaft profile 13 which is not rotationally symmetrical but is point-symmetric. The unround shaft profile 13 of the measuring section 11 projects here radially beyond the circular cross section of the shaft 10 which is illustrated in section, but could also radially recoil with respect to the cross section of the shaft 10 or could be formed in a manner radially flush with the shaft 10. The shaft 10 and the measuring section 11 are made from metal here, that is to say are electrically conductive, in particular. The shaft profile 13 is in the form of a toothed profile which has four measuring elevations 14 which are uniformly distributed over the circumference. The measuring section 11 is arranged in such a manner that the measuring elevations 14, as out-of-roundnesses according to the disclosure interact with the electric field EF, in particular if a measuring elevation 14 passes the electrodes 20, 30 on account of a rotational movement of the shaft 10, as illustrated in FIG. 1B. A change in the electric field EF is caused by the rotation of the unround measuring section 11.

[0048] The electrodes 20, 30 are arranged on a printed circuit board 50 which is made from an electrically insulating material, for example from plastic, and has a circular measuring recess 51 into which the measuring section 11 extends. The electrodes 20, 30 are conductively connected, via conductor tracks 21 and 31, to a microcontroller 70 which is in turn conductively connected to an evaluation unit 40 and is supplied with electrical power by a voltage source 60. The microcontroller 70 and the evaluation unit 40, which comprises a filter unit 80, preferably a bandpass filter, are likewise arranged on the printed circuit board 50.

[0049] In the case of a rotation of the shaft 10, which is connected to the measuring section 11 in a rotationally fixed manner or in one part, each out-of-roundness of the measuring section 11 causes a change in the electric, preferably electrostatic, field EF which is generated in the environment of the electrodes 20, 30. This change in the electric field EF can be capacitively captured, as a capacitance change of the capacitor formed by the electrodes 20, 30 together, by the evaluation unit 70. For example, a voltage, preferably a uniformly pulsed DC voltage, for example in the form of square-wave pulses with a voltage amplitude of 0 V and 5 V, is applied to the first electrode 20 through an output of the microcontroller 70. A corresponding electric field EF is generated. If a measuring elevation 14 moves through the electric field EF, that is to say rotates through the electric field, the result is a change in the capacitance of the capacitor formed by the capacitor elements of the electrodes 20, 30. This capacitance change can be measured, for example by means of a voltage change at the second electrode 30, which can be tapped off at an input of the microcontroller 70. The evaluation unit 40, which could also be integrated in the microcontroller 70, captures the change in the electric field EF as a countable signal change or fluctuation, in particular in the form of a rise or fall in a voltage signal. The rotational position and/or the speed of the shaft 10 can be determined by capturing the number of changes, in which case the number of available measuring elevations 14 of the measuring section 11 is preferably stored in the evaluation unit 40.

[0050] FIG. 2 shows an embodiment of a measuring arrangement 100 according to the disclosure having two electrode pairs 91, 92 each with first electrodes 20 and second electrodes 30. The electrode pairs 91, 92 are arranged in an offset manner with respect to one another based on the circumference of the shaft 10. On the one hand, this makes it possible to increase the accuracy with which the rotational position and/or speed is/are determined. On the other hand, the direction of rotation of the shaft 10 can be additionally determined, in particular by capturing the sequence of the temporally offset change in the electric field EF by means of the first electrode pair 91 and the second electrode pair 92. Depending on the direction of rotation, a particular measuring elevation 14 causes a change in the electric field EF first of all with respect to the first electrode pair 91 and, in a temporally offset manner, with respect to the second electrode pair 92, from which the direction of rotation of the shaft 10 can be determined.

[0051] A measuring arrangement 100 according to the disclosure can be easily implemented and is suitable, in particular, for use for determining the rotational position, speed and/or direction of rotation of a shaft of an electric motor of electromotively adjustable devices of a vehicle, for example a sliding roof, a window lifter, an exterior mirror, a seat, convertible roof or a locking mechanism.

[0052] It should be pointed out at this point that all aspects of the disclosure which have been described above are claimed as being essential to the disclosure alone and in any combination, in particular the details illustrated in the drawings. A corresponding situation applies to the method steps explained. Modifications thereof are familiar to a person skilled in the art.

LIST OF REFERENCE SIGNS

[0053] 10 Shaft [0054] 11 Measuring section [0055] 12 Shaft axis [0056] 13 Shaft profile [0057] 14 Radial measuring elevation [0058] 20 First electrode [0059] 21 Conductor track [0060] 30 Second electrode [0061] 31 Conductor track [0062] 40 Evaluation unit [0063] 50 Printed circuit board [0064] 51 Measuring recess [0065] 60 Voltage source [0066] 70 Microcontroller [0067] 80 Filter unit [0068] 91 First electrode pair [0069] 92 Second electrode pair [0070] 100 Measuring arrangement [0071] EF Electric field [0072] PM Central plane [0073] PE Electrode plane